Alopecia areata

In most people with alopecia areata, hair falls out in small, round patches, leaving coinsized areas of bare skin. This patchy hair loss occurs most often on the scalp but can affect other parts of the body as well. Uncommonly, the hair loss involves the entire scalp (in which case the condition is known as alopecia totalis) or the whole body (alopecia universalis). Other rare forms of alopecia areata, which have different patterns of hair loss, have also been reported.

Hair cycle 1) Anagen: the active phase of hair production. can reach 5 years, (85%) 2) Catagen: a short phase of conversion from active growth to the resting phase. (10-14 days) 3) Telogen: a resting phase at the end of which the club hair is shed. (2-3months)(15%) Hairs are classified into three main types.  Lanugo hairs: fine long hairs covering the fetus, but shed about 1 month before birth.  Vellus hairs: fine short unmedullated hairs covering much of the body surface. They replace the lanugo hairs just before birth.  Terminal hairs: long coarse medullated hairs seen, for example, in the scalp or pubic regions. Their growth is often influenced by circulating androgen levels.
 It's loss of hair  Local V.S. Diffuse  Alopecia areata: also known as spot baldness, is a condition in which hair is lost from some or all areas of the body. Often it results in a few bald spots on the scalp, each about the size of a coin.

Alopecia Areata
• lifetime risk of getting alopecia areata is 2% • Pathophysiology: immunological basis is suspected because of an association with autoimmune diseases such as Hashimoto's thyroiditis, atopy, vitiligo, IBD, autoimmune poly endocrinopathy syndrome. • Histologically: T lymphocytes cluster around affected hair bulbs • Causes : -Inherited as a complex genetic trait, sometimes HLA-DQ3, -DR11 or -DR4 , with an increased occurrence in 1 st degree relatives. Also 10% of patients with Down's syndrome (involvement of genes on chromosome21) -Environmental factors
 !!!: They are broken off about 4 mm from the scalp, with the proximal end more narrowed and less pigmented Patches are most common in the scalp and beard. Up to 50% of patients show fine pitting or wrinkling of the nails.
Course: The outcome is unpredictable. In a first attack, regrowth is usual within a few months. New hairs appear in the center of patches as fine pale down, and gradually regain their normal thickness and color, although the new hair may remain white in older patients. 50% of cases resolve spontaneously without treatment in 1 year, and only 10% go on to develop severe chronic disease. Subsequent episodes tend to be more extensive and regrowth is slower.

Telogen effluvium
Telogen effluvium : a scalp disorder characterized by the thinning and shedding of hair resulting from early entry of hair in the telogen phase.

 Cause
Telogen effluvium can be triggered by any severe illness, particularly those with bouts of fever or haemorrhage, by childbirth and by severe dieting . large numbers of hairs are lost at the same time in the telogen phase.  Presentation and course The diffuse hair fall , 2-3 months after the provoking illness, can be mild or severe. Beau's lines may be seen on the nails. Regrowth, not always complete, usually occurs within a few months.

DDx. :
 androgenetic alopecia (females the onset is gradual in mid adulthood, and hairs remain rather firmly anchored to the scalp)  diffuse alopecia areata (hair loss is more patchy, & the onset abrupt with waxing & waning. Shedding may be prominent. Exclamation mark hairs are often present.)

Treatment:
 This condition is unaffected by therapy, but patients can be reassured that their hair loss will be temporary.